The invention is related to the field of data storage systems.
Many modern computing installations utilize large, sophisticated data storage systems having a desired degree of overall size or capacity, reliability/availability, and performance. Examples of such large data storage systems include those used in connection with large corporate databases or large public or private web sites. These storage systems employ an array of relatively independent individual disk drives along with data communications devices and interconnections to provide desired data accessibility. The number of individual disk drives may be in the range of tens to hundreds, collectively providing many gigabytes or terabytes of storage capacity.
It is known to provide redundancy in data storage systems to protect user data from loss upon failure of disk drives or other storage system components. One general class of data protection schemes is referred to by the acronym RAID, which stands for “redundant array of independent disks”. Different forms of RAID provide data protection in different ways. In one form, data is replicated or “mirrored”, and upon failure of a primary device, data is obtained from a mirror device. Other forms of RAID employ redundancy in the form of parity that is stored in association with data. When all or part of a disk drive fails, the data that was stored on the disk drive is re-created from related data and parity information. Data loss is avoided in a fairly storage-efficient manner.